1. Field of the Invention
The present invention relates to a video signal reproducing apparatus, and more particularly to an apparatus for reproducing video signals representative of a movie image to which control information is added for every image plane.
2. Related Background Art
As a system for compression-encoding a movie image with high efficiencies, a system which utilizes a correlation between fields or frames, that is, in the direction of time axis has been developed. In such encoding system as this, since the correlation in the direction of time axis is generally high in a still image or the image which has little movement, high efficiencies will be obtained for the case where the encoding is performed based on the image information of the past. However, since the correlation in the direction of time axis becomes low for the image which moves violently, it is a general practice to perform the encoding according to the processing only within the field/frame. Decision for such encoding may generally be effected by detecting the movement of input images at the time of encoding. Upon transmission of a movie image signal encoded as above, it is a general method to transmit the detected movement information as additional data (hereinafter also referred to as movement data) which is part of control information needed at the time of encoding by use of a data format added to the image data.
As this type of movie image encoding system, a MUSE (Multiple Sub-Nyquist Sampling Encoding) system is known. A control signal included in a MUSE signal contains movement information such as mode information, magnitude information representing the degree of movement, and direction information representing the direction of movement, and the encoding of the MUSE signal is performed based on these movement information. That is, mode data is produced through mode judgement for a still mode (still image plane), a movie image mode (movie image plane) and a scene change mode, movement vector data is produced based on the magnitude information and the direction information, and the encoding is performed according to these mode data and movement vector data. These mode data and movement vector data are added to movie image data in every field. This added data is used for adaptive processing at the time of decoding. By the way, the abovementioned movement vector data is formed to perform the encoding by using the image data of the previous image plane despite the movie image mode, in the event of uniform movement due to panning or the like of a camera, and added to the encoded movie image data.
The movement data generated when the movie image signal is encoded will be herein explained in detail in conjunction with FIG. 1. In this figure, N, N+1, N+2 and N+3 diagrammatically represent successive field image planes in the video signals indicative of movie image. The mode data and movement vector data that are movement data used for encoding such successive field image planes are shown respectively at the under side of each image plane. For simplicity of explanation, it is assumed that patterns before N and after N+3 are at rest with respective similar patterns and there are three types of modes, that is: a still mode in which a still image continues; a movie mode in which there is any movement within the image plane; and a scene change mode in which the pattern changes to an entirely different pattern, and it is also assumed that the movement vector has a value of horizontal direction x and of vertical direction y when there was an uniform movement within the image plane. Hereinafter, the same applies to examples described in the text.
In the first image plane indicated by N, since the preceding condition is assumed to be a still image plane, it corresponds to a still mode, and the movement data specified as movement vector is (0, 0). In the next image plane represented by N+1, it changes to a movie mode provided that there was a partial movement within the image plane, but the movement vector remains unchanged (0, 0). In the image plane indicated by N+2, the mode remains in the movie mode, but the movement vector changes to (x, y) provided that there was an uniform movement due to the panning or tilt of the camera. In the still another image plane indicated by N+3, it changes to a scene change mode provided that the pattern has changed to an entirely different pattern and the movement vector becomes (0, 0).
Shown in the upper part of FIG. 2 are the results of encoding process of the movie image based on the movement data generated as mentioned above. Assume that n, n+1, . . . are movement data corresponding to the image data Dp in each field shown by N, N+1, . . . , and also correspond to the mode and movement vector in FIG. 1. In addition, in the abovementioned MUSE system, when the image data Dp is recorded in the order shown by N, N+1, . . . , the format of transmission signal will become such a format that can be obtained by adding the movement data corresponding to the image data Dp in the subsequent field to the image data Dp in each field, but the movement data in the figure is shown as one to which the corresponding image data Dp is added, for the sake of simplicity of explanation.
If the transmission signal formatted as described above and recorded in an image recording-reproducing apparatus is reproduced in the order different from that used at the time of recording such as in the case of reverse reproduction, for example, the combination of the image data Dp and the movement data Dm will be reproduced without any change as shown in the lower part of FIG. 2. Because of this, if the image data Dp in each field recorded in the order of N, N+1, . . . , as shown in FIG. 1 is reproduced in the reverse order, they would be reproduced in the order of N+3, N+2, N+1 and N as shown in FIG. 3, and the movement data Dm takes the specific form that is shown in the lowermost part of FIG. 3 and different from the intrinsic form shown in the middle part thereof.
As discussed above, in the case of the conventional movie image signal reproducing apparatus, the movement data obtained through the reproduction of movie image in the order different from that used at the time of recording, as in the event of reverse reproduction, may differ from the intrinsic movement data, so that the movement data can not be correctly reproduced and a malfunction may occur in the encoding operation, thus leading to any degradation in image quality.
In addition, in the apparatus for recording and reproducing such MUSE signal as this, the output reproduced under the state of normal reproduction (i.e., reproduction at the same speed as that used for recording) is the MUSE signal itself. In order to obtain an original high grade television signal, the reproduced MUSE signal must be decoded by a MUSE decoder. Decoding of the MUSE signal by means of the MUSE decoder is performed with subsampling information that is included in the MUSE signal as control signal.
The control signal in the MUSE signal consists of 32 bits labeled as bit #1-bit #32, of which the bit #9 shows a subsample phase of luminance signal in each field, and the bit #10 prescribes a subsample phase of macro signal. In addition, the bits #16, 17, 18 show movement information, the bit #0 corresponds to normal, the bit #1 shows a perfect still image, the bit #2 shows a semi-still image, the bit #3 corresponds to scene change, and the bits #4-#7 show the degree of movement.
FIG. 4 is a diagram useful for explaining a subsampling pattern of the MUSE signal, wherein the pixels indicated by .largecircle., .quadrature., and represent the pixels sampled in respective fields defined as 4n, (4n+1), (4n+2) and (4n+3). "n" is any integral number above 0, and the number of each field is denoted as field #4n, field #(4n+1), etc.
However, assuming now that the MUSE recording-reproducing apparatus is operated in the reproduction mode at a speed different from that used for recording, the reproduced output becomes a signal which is far apart from a perfect high grade television signal which can be obtained only by making the round of four fields. In general, in the case of slow reproduction mode at a speed of 1/k, the MUSE signal of one field is repetitively outputted extending over k fields. FIG. 5 shows one example of a sampling pattern of the reproduced output obtained by reproducing the signal of sampling pattern in FIG. 4 under a slow reproduction mode at a speed of 1/2. As shown in the drawing, the data of field #4n is repetitively outputted extending over two fields. Like these, the data of field #(4n+1), #(4n+2) . . . is outputted extending over two fields, respectively.
In short, in the case of slow reproduction at a speed of 1/2, the data for two fields only of 4 field periods is outputted. Accordingly, the MUSE decoder restores a high grade television signal from the data of two fields through still image processing or movie image processing. In the case of still image processing by the MUSE decoder, the data on the upper line for every one sample is used for the odd-numbered fields (lines 7, 48, . . . , 562: luminance signal) and the data that must be intrinsically located in the tilt direction may be positioned adjacent to the horizontal direction, thus leading to the degradation in image quality. Whereas, in the case of movie image processing, the image will become obscured, thus making prominent in the event of slow reproduction.